An ink jet printing apparatus that forms an image by ejecting ink from a print head onto a print medium can form a high-resolution image using a small print head having a plurality of nozzles arrayed at high density. The ink jet printing apparatus can also realize a color printing with a relatively inexpensive, compact construction that comprises a plurality of print heads and supplies a plurality of different color inks to the respective print heads. Therefore the ink jet printing apparatus is currently used in a variety of image output devices, such as printers, facsimiles and copying machines, whether for business use or for home use.
In such an ink jet printing apparatus, it is important to maintain the ink in the print head at a constant negative pressure to stabilize the ink ejection operation of the print head. For this purpose, it is common practice to provide a negative pressure generation means in an ink supply system and supply the ink given a negative pressure by the negative pressure generation means to the print head.
One of such conventional negative pressure generation means utilizes a capillary attraction of a sponge-like ink absorber installed in an ink tank to generate a negative pressure (for example, Patent Document 1).
Another example has at least a part of the ink tank formed of a flexible member and biases the flexible member outwardly of the ink tank by a bias means such as spring in order to keep an interior of the ink tank at a negative pressure (for example, Patent Document 2).
Still another example has an ink tank disposed at a position lower than the print head and utilizes a water head difference to apply a negative pressure to the ink (for example, Patent Document 3).
The ink applied with a constant negative pressure by the negative pressure generation means is supplied to the print head, as if it is drawn into the print head, by a pressure difference between its negative pressure and a negative pressure in the print head that increases as the ink ejection proceeds. The interior of the print head is therefore maintained at a constant negative pressure.
Patent Document 1: Japanese Patent Application Laid-open No. 07-068776
Patent Document 2: Japanese Patent Application Laid-open No. 2001-315350
Patent Document 3: Japanese Patent Application Laid-open No. 06-183018